Directional drilling has dramatically changed the landscape of large-scale drilling operations. In common practice today are both the Logging-While-Drilling (LWD) and Measurement-While-Drilling (MWD) configurations, each permitting enhanced control, monitoring and information collection with respect to the subject formation.
With LWD and MWD, a wide range of measurements of formation properties are made during the drilling operation. Examples of properties measured include, but are not limited to resistivity, porosity, sonic velocity, gamma ray levels, as well as pressure and temperature of the well bore. Moreover, MWD permits the measurement of well bore trajectory using a range of detectors such as accelerometers and magnetometers. With the use of telemetry technologies including mud pulse and electromagnetic (EM) telemetry, the data is sent back to the surface to the operators. With this information, the operator is able to accurately guide a drill string to a predetermined target.
Directional drilling provides many advantages over more conventional drilling methodologies. In particular, directional drilling provides a more environmentally conscience approach to drilling as it minimizes surface disruptions by requiring a much smaller footprint on a given drill site. So versatile is directional drilling that well sites can be located outside of an environmentally sensitive or protected area. Directional drilling also makes it possible to expand upon existing vertical wellbores by drilling laterally away to offset targets, thereby maximizing production from a single formation.
As can be appreciated, with the incorporation of electronics in the tool string, power supply issues plague the industry. Various solutions have been presented, with the more conventional approaches using surface-based wire-line electrical connections as well as the incorporation of batteries (i.e. lithium-thionylchloride) into the downhole tool-string. Each of these power supplies has its shortcomings, whether it is safety, stability, durability or overall cost.
Alternate power generation methodologies have been developed and implemented to varying degrees of success. In particular, a number of power generators have been developed which are based on harnessing the flow of drilling mud to rotate a downhole power generator. An example of this technology includes U.S. Pat. Nos. 5,839,508 and 6,672,409.
U.S. Pat. No. 5,839,508 pertains to an electrical generating apparatus which connects to the production tubing of a drilling operation. In a preferred embodiment, this apparatus includes a housing having a primary flow passageway in communication with the production tubing. The housing also includes a laterally displaced side passageway communicating with the primary flow passageway such that production fluid passes upwardly towards the surface through the primary and side passageways. A flow diverter may be positioned in the housing to divert a variable amount of production fluid from the production tubing and into the side passageway. An electrical generator is located at least partially in or along the side passageway. The electrical generator generates electricity through the interaction of the flowing production fluid.
In U.S. Pat. No. 6,672,409, a generator assembly for generating power in the downhole end of a drill string is disclosed. The drill string provides a fluid passageway in which a downhole generator is positioned so as to subject a rotatable turbine to a pressurized fluid flowing in the fluid passageway, thereby imparting a mechanical rotation to the turbine. The turbine is coupled to a generator so that the mechanical rotation of the turbine is transferred to a power output of the generator.
In use, many of the prior art methodologies for generating power downhole are limited by various deficiencies and/or drawbacks. Problems encountered include, for example, safety issues, mechanical complexity and durability, as well as overall cost. As a result, there is an ongoing demand for alternatives to the aforementioned technologies that offer improved performance, greater reliability as well as reduced complexity and overall cost.